Bubble nucleation in rhyolitic melts: Experiments at high pressure, temperature, and water content

摘要: Abstract We report the first measurement of bubble nucleation in hydrated rhyolitic melts response to pressure release. Two obsidians, one containing less than 1% microlites Fe—Ti oxides and other about 20% various crystals were at 150 MPa 780–850°C. After saturation was reached (5.3–5.5 wt% water), lowered samples allowed nucleate grow bubbles for amounts time, before final, rapid quenching experiments. The results demonstrate importance heterogeneous nucleation. Microlites are very efficient as sites In their presence, modest observed even after decompression by 6 –10 8 cm −3 ). absence microlites, no occurred ΔP MPa. At > 10 MPa, also nucleated on biotite, zircon apatite. Modest (10 3 5 ) took place crystal-free samples, but it still heterogeneous. When exceeded 80 became extensive 7 lack correlation density with either time or suggests that Nucleation rates controlled mainly availability sites. Rates faster s −1 when present, 70 Narrow size distributions most immediately drop. experimental data we present here indicate presence can lead two distinct modes formation. a large number (e.g., oxide) requires little supersaturation, good approximation, gas magma equilibrium. magmas contain inefficient nucleating bubbles, high degrees supersaturation required order initiate These exsolution may contrasting styles convection, build up eruption.